The present invention relates to a liquid crystal display (LCD) projector in which an output of a light source is set selectively.
An LCD projector is known from, for example, Japanese Patent Laid-Open Publication No. 5-313115 (1993). FIG. 14 shows a basic construction of this known LCD projector. In FIG. 14, a main power source 210 supplies electric power to an on-off switch 220 for turning on and off a light source 230. The known LCD projector further includes a condensing lens 240, an LCD panel 250 acting as an image forming member, a projecting lens system 260 and a screen 270.
A halogen lamp or the like is used as the light source 230. A light ray from the light source 230 not only is condensed but is converted into collimated rays by the condensing lens 240. The collimated rays are supplied from the condensing lens 240 to the LCD panel 250 in which an image is formed. Subsequently, the image of the LCD panel 250 is projected onto the screen 270 through enlargement by the projecting lens system 260 such that an enlarged image is formed on the screen 270.
As the voltage is applied across the thickness direction of the LCD panel 250, the rate of transparency T varies in an S curve as shown in FIG. 15.
Generally, in an LCD projector, it is often desirable to change luminance of a light source in accordance with its user""s preference or brightness of a room in which the LCD projector is installed. For example, if luminance of the light source is reduced in accordance with the factors referred to above, service life of the light source can be lengthened as compared with a case in which the light source is driven at its maximum luminance at all times.
However, in the known LCD projector of FIG. 14, it is impossible to change luminance of the light source 230. Namely, in this known LCD projector, since the light source 230 is driven at its maximum luminance at all times, luminance of the light source 230 gradually drops merely upon lapse of integrated on-state period of the light source 230 as shown in FIG. 16. Therefore, the known LCD projector has such disadvantages that service life of the light source 230 is short and electric power consumed by the known LCD projector is large.
Accordingly, an object of the present invention is to provide an LCD projector in which service life of a light source is lengthened and electric power consumed by the LCD projector is saved.
In order to accomplish this object of the present invention, an LCD projector according to the present invention comprises: a power source; an image data source for producing an image data; a light source which is able to provide different levels of power; an LCD panel for modifying a light ray from the light source in accordance with said image data to produce light rays of an image; a projecting lens for projecting the light rays from the LCD panel onto a screen through enlargement; a control circuit for controlling an output of the power source so as to selectively set an output power: and a correcting circuit for correcting an image data before being supplied to the LCD panel so as to compensate the disturbance of the white balance caused by the change of the power of the light source.
The correcting circuit further corrects said image data so as to compensate the light intensity change caused by the intrinsic transparency characteristics of the LCD panel.
In accordance with the present invention, since luminance of the light source is changed in accordance with a user""s preference or brightness of a room in which the LCD projector is installed, service life of the light source can be lengthened and electric power consumed by the LCD projector can be saved.